How to Enable Hidden Dock Stack Gestures in Mac OS X
This is a neat little hack that lets you activate any stack within the Mac Dock by hovering over it and making the scroll gesture on a multitouch trackpad or Magic Mouse, or by rolling the scroll wheel on a mouse.
Do the same trick while hovering the mouse cursor over an app icon in the Dock, and App Exposé will activate. You will see open program windows for that particular app and—with compatible apps—the app’s document history. This is similar to the App Exposé option within the More Gestures section of the Trackpad entry within System Preferences.
However, in each case, once you’ve activated the secret setting, you need to scroll up to activate (that is, to make the stack expand), and then scroll down to deactivate (to make the stack hide again). You’ll need to scroll a substantial amount to activate the feature so that Mac OS X knows you’re doing it on purpose and not accidentally. In other words, you’ll need to flick the scroll wheel up rather than just rotate it a few clicks.
How to Enable a Hidden Dock Stacks Gesture on Mac
To activate this hidden feature, open a Terminal window and type the following:
defaults write com.apple.dock scroll-to-open -bool TRUE;killall Dock
The changes take effect immediately.
How to Disable Scroll to Open Gesture for Dock Stacks
To deactivate this feature, open a Terminal window and type the following:
defaults delete com.apple.dock scroll-to-open;killall Dock
You’ll be back to the default setting.
This is another awesome tip from Keir Thomas, the author of a new book called Mac Kung Fu, which contains over 300 tips and tricks for OS X Lion. He’s the same guy who discovered the iTunes “Now Playing” notification tip and the Quick Look select text tip.